docs: mark GeoEdge.discord as design-branch-only, not on dev

The line references were correct but silently implied the code was on dev.
It is on design/correspondence-and-censorship (a8845e1). On dev,
co_registration is still at engram_geometry.h:79 with its original comment
and still unread by anything.

engram/spec/cognitive-architecture.design.md

@@ -584,7 +584,9 @@ Consequences, all of which are *features*:
   >
   > The disagreement therefore goes back on the edge, where the loop that computed
   > the aggregate already had both halves and discarded them
-  > (`lang/runtime/engram_geometry.h:43–47`, `engram_geometry.c:454–473`):
+  > (**not on `dev`** — branch `design/correspondence-and-censorship`, commit
+  > `a8845e1`: `lang/runtime/engram_geometry.h:43–47`,
+  > `engram_geometry.c:454–473`):
   > `discord = z(semantic proximity) − z(association strength)`, standardized within
   > the region from accumulators already gathered — no second statistic, no
   > constant, **no threshold**. `|discord|` *is* the nucleation strength and raises